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一 Windows Batch

1) 如果变量的值来自文件，则必须类似set /p num=<num.txt 。
2）如果变量的值想来自命令的结果，则一些命令可以使用%%，例如set bbb=%time%，set aaa=%date%。对于一般的命令只能先输出到临时文件，然后再读入，例如time /t > ddd.txt set /p ddd=<ddd.txt。
3) 在for中可以使用命令，例如·time /t·。

实例：

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rem the num.txt file only contains one line "001".
echo work well
echo %num%
echo doesn't work
echo %num%
echo %num%
echo %num%
echo %num%
echo get value from command

echo %bbb%
echo %aaa%
echo general command doesn't work
echo %ccc%
echo one solution is to output the result to txt and then input it
set/p ddd=<ddd.txt
echo %ddd%
echo special